A voltage of signals transferred between semiconductor devices, namely, an interface (I/F) voltage has been decreased from the viewpoint of power consumption. For example, a voltage of signals input to or output from a semiconductor memory (e.g., DRAM) is lower than or equal to 1.8 V. Further, a data transfer rate exceeds 2 Gbps per signal pin. This means that elements forming input/output circuits are required to be low-voltage (low-withstand voltage) and have high operational speed. Accordingly, it is important for semiconductor devices to satisfy this request. On the other hand, in opposition to the decrease in the interface voltage, there is still a request in the market for using semiconductor devices of conventional interface voltage (e.g., 3.3 V). This request is generated from the preservation of compatibility with semiconductor devices of old interface standards.
In order to satisfy these two requests, there may be a method to prepare elements specialized in each request in the manufacturing process. However, the manufacturing process has become complicated in accordance with the miniaturization. Therefore, a very high manufacturing cost is needed to enable the above method.
As described above, a semiconductor device including only low-withstand voltage elements is requested to have a high-voltage I/F. This request can be realized by a level conversion circuit which includes only low-withstand voltage elements and is compatible with a high-voltage and high-speed operation. However, among the level conversion circuits having been proposed hitherto, there is none that simultaneously satisfy an increase in speed and the withstand voltage. Because of this, there has been a demand for a level converter to have both high speed and low withstand voltage.
Further, in the interface equipment with various SD cards, there is a case where the voltage of the interface is changed between the data read operation and the data write (storage) operation. In such a case, it is desirable to be able to deal with the case by changing only the power source voltage to be supplied without changing the circuit.